Craniofacial malformations constitute approximately one-third of all congenital birth defects. These anomalies are largely attributed to abnormalities in neural crest cells which are a migratory population of stem and progenitor cells. The neural crest gives rise to cartilage, bone, and connective tissue in the head, neurons and glia of the peripheral nervous system and portions of the heart outflow tract. Proper head and facial development requires the coordinated integration of neural crest cell formation, migration and differentiation with extrinsic patterning cues derived from the surrounding mesoderm, ectoderm and endoderm. We propose that the cranial mesoderm and the vascular network it generates are instrumental in patterning neural crest cells during craniofacial development. Moreover, the forkhead/winged-helix transcription factors FoxC1 and FoxC2 which are expressed in the cranial mesoderm mediate the extrinsic patterning of neural crest cell development. Therefore in Aim 1 we will characterize the aspects of neural crest cell patterning;formation, proliferation, migration and/or differentiation that are dependent upon FoxC signaling. In Aim 2 we will determine the role of FoxC signaling in cranial mesoderm development and vascular remodeling and correlate this with disruptions in neural crest cell development. In Aim 3 we will attempt to rescue the mesoderm/vascular defects associated with haploinsufficiency of FoxC genes and prevent the neural crest cell anomalies associated with the pathogenesis of craniofacial defects. This proposed study will highlight the importance of extrinsic patterning signals on neural crest and therefore craniofacial morphogenesis and also help to explain the high incidence of head and facial anomalies associated with congenital birth defects. Relevance: Development of the vertebrate head is a complex process requiring interaction between multiple specialized tissues, and malformation of the head and face are associated with a large number of congenital disorders. Although the majority of the tissues of the head are derived from neural crest cells, recent studies have revealed that the environment surrounding these cells influence their patterning and development. The proposed study will identify these external factors and help explain the sensitivity of neural crest cells to malformation and the high incidence of congenital craniofacial birth defects.